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  1. /*
  2.           ********
  3.     *******      *******
  4.       ******    ******
  5.          ****  ****
  6.              **
  7. */
  8.  
  9. #include<bits/stdc++.h>
  10. using namespace std;
  11.  
  12. typedef long long ll;
  13. #define el '\n'
  14.  
  15. const ll MOD = 998244353;
  16. const ll N = 200005;
  17.  
  18. ll n;
  19. ll f[N] , inv[N];
  20.  
  21. ll power(ll b , ll e)
  22. {
  23.     ll res = 1;
  24.     b %= MOD;
  25.     while(e > 0)
  26.     {
  27.         if(e % 2 == 1) res = (res * b) % MOD;
  28.         b = (b * b) % MOD;
  29.         e /= 2;
  30.     }
  31.     return res;
  32. }
  33.  
  34. void pre()
  35. {
  36.     f[0] = 1;
  37.     inv[0] = 1;
  38.  
  39.     for(int i = 1 ; i < N ; i++)
  40.     {
  41.         f[i] = (f[i - 1] * i) % MOD;
  42.     }
  43.  
  44.     inv[N - 1] = power(f[N - 1] , MOD - 2);
  45.  
  46.     for(int i = N - 2 ; i >= 1 ; i--)
  47.     {
  48.         inv[i] = (inv[i + 1] * (i + 1)) % MOD;
  49.     }
  50. }
  51.  
  52. ll nck(ll n , ll k)
  53. {
  54.     if(k < 0 || k > n) return 0;
  55.     return f[n] * inv[k] % MOD * inv[n - k] % MOD;
  56. }
  57.  
  58. signed main()
  59. {
  60.     ios_base::sync_with_stdio(0);
  61.     cin.tie(0);cout.tie(0);
  62.  
  63.     freopen("wonderful.INP" , "r" , stdin);
  64.     freopen("wonderful.OUT" , "w" , stdout);
  65.  
  66.     pre();
  67.  
  68.     cin >> n;
  69.  
  70.     ll ans = 0;
  71.     for(int i = 1 ; i <= n ; i++)
  72.     {
  73.         ll c1 = (n - i + 1) % MOD;
  74.         ll c2 = (1 - ((i - 1) % MOD) * ((n - i) % MOD)) % MOD;
  75.         ll ci = (c1 * c2) % MOD;
  76.  
  77.         if(i % 2 == 0) ci = -ci;
  78.         ci = (ci % MOD + MOD) % MOD;
  79.         ans = (ans + ci * f[n - i]) % MOD;
  80.     }
  81.  
  82.     cout << ans;
  83.     return 0;
  84. }
  85.  
  86. /// LeviHanlde
  87. /// みなさん、こんにちは！
  88.  
Success #stdin #stdout 0.01s 6808KB
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https://ideone.com/Ctoxui
language:
C++14 (clang 8.0)
created:
3 days ago
visibility:
public

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